A tandem-type image forming apparatus can include photoconductors, which are provided individually for respective colors (such as black, cyan, magenta and yellow). The photoconductors are arranged along the rotational direction of a paper conveyor belt, so that images of respective colors held on the photoconductors can be sequentially transferred to paper on the belt.
A resultant color image formed by the tandem-type image forming apparatus may include a color shift, due to displacement of images of respective colors from one another. In view of this, some of image forming apparatuses have a function for aligning the forming positions of images of respective colors.
During the alignment function being performed, the image forming apparatus forms a registration pattern (i.e., a pattern used for alignment) on the belt, so that an estimated displacement amount of an image formed of each color can be determined based on the registration pattern. The displacement of an image formed of each color is corrected based on the estimated displacement amount.
However, the estimated displacement amounts may fail to be determined accurately in some circumstances, resulting in inaccuracy in final displacement correction.